1.用戶保存數據后

2.Web卸載頁面后

3.費時操作前。

原理：費時操作時間較長，用戶感覺不到垃圾收集占用的時間。


GC.Collect 對指定代齡對象強制執行垃圾回收
GC.MaxGeneration 查詢托管中最大的代齡
GC.GetGeneration 查詢對象的齡


using System;
using System.IO;
namespace TestDisp
{
	
	class GenObj
	{
		~GenObj()
		{
			Console.WriteLine("In Finalize method");
		}
	}
	class Class1
	{
		[STAThread]
		static void Main(string[] args)
		{
			Console.WriteLine("Maximum generations:"+GC.MaxGeneration);

			Object o=new GenObj();

			Console.WriteLine("Gen "+GC.GetGeneration(o));

			GC.Collect();

			Console.WriteLine("Gen "+GC.GetGeneration(o));

			GC.Collect();
			Console.WriteLine("Gen "+GC.GetGeneration(o));

			GC.Collect();
			Console.WriteLine("Gen "+GC.GetGeneration(o));

			o=null;
			
			Console.WriteLine("Collecting Gen 0");
			GC.Collect(0);
			GC.WaitForPendingFinalizers();

			Console.WriteLine("Collecting Gen 1");
			GC.Collect(1);
			GC.WaitForPendingFinalizers();

			Console.WriteLine("Collecting Gen 2");
			GC.Collect(2);
			GC.WaitForPendingFinalizers();
			
		}
	}
}